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113
Another indispensable part of modern amenities is gas supply. It has
come now to be of a very wide use. With an intensive exploration of finding
natural gas it has gradually replaced the manufacture in its utilization. At the
present time natural gas is put to large-scale economic use. The principal utili-
zation of natural gas is as a clean, convenient, economical source of heat. In
homes it is used for cooking, water heating, refrigeration for food as well as for
space heating. Nowadays most of the homes are heated by natural gas and the
number of gas-supplied homes was increasing at a rate limited chiefly by the
ability of the steel industry to produce the pipe through which the gas is trans-
ported. Natural gas supply is used also as a heat source in commercial establish-
ments such as restaurants and bakeries for cooking and in stores, offices and
other commercial buildings for heating and comfort cooling.
Principles of air-conditioning
The term air-conditioning has been so widely and loosely used that the
student should be careful in trying to understand its true meaning. For many
years we have introduced air into buildings after heating, dehumidifying and, in
some cases, cooling it, and we have called that process ventilation. In recent
years much greater stress has been laid on the treatment of air as compared with
circulating it merely through the building, and we now call the process air-
conditioning. Air-conditioning, then, may be said to be the treatment of the air
in the building so as to make it more comfortable or healthful for human beings
or more suitable for manufacturing processes.
The factors which are of importance in air-conditioning are many, and un-
fortunately the term is sometimes used to refer only to minor factors such as
cleaning and circulating of air. It is important that the engineer should exactly
realize what an air-conditioning system does and what it does not do, and that
he should make clear
to others what results can be expected from the system.
Complete air-conditioning is known to involve the simultaneous control
of the following factors: temperature, humidity, air motion, air distribution,
dust, bacteria, odours, toxic gases. Of these the first three, temperature, humid-
ity and air motion, are most important, and no air-conditioning system deserves
the name unless it satisfactorily controls those three factors. Thus it follows that
air-conditioning involves heating as well as cooling.
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